This invention concerns the control of the head position of a disk drive device. More precisely, it concerns the conversion of the logical address (which is contained in an access command that has been issued by an upper level device) to the physical address on the disk.
As the capability of processors and the popularity of multimedia have both increased, there has been a greater demand for faster processing speeds and for larger capacities for disk drive devices (which are the external storage devices for computers). In order to increase the storage capacity of disk drives, a plurality of disks are normally provided in each drive. Each disk drive also includes a plurality of heads for recording or regenerating signals, where one head is provided for each disk recording surface.
In order to identify the position on a disk where data will be recorded, the disk is assigned physical addresses that indicate physical locations on the disk. The locations where data are stored upon the disk are identified by: (1) a sector address that identifies the circumferential location on a track; (2) a cylinder address that identifies the radial location on a disk; and (3) a head address that identifies which recording surface on which of the many disks will be used. In response to a disk access request from an upper level device, a logical address, which is controlled by the upper level device, must be correlated to the physical address on the disk. The disk drive device includes memory reserved for a conversion table that converts the logical addresses into the physical addresses.
FIG. 1 shows a cross-section of a disk. In a disk drive device that has a plurality of disks (x number of disks), the physical addresses may be assigned as indicated in FIG. 1. That is, disks 1-1 to 1-x are stacked on the same axis. The head addresses are assigned in sequence starting from the very top disk, from 0, 1, 2, 3, 4, . . . to 2xxe2x88x922, 2xxe2x88x921, as shown in FIG. 1. The cylinder addresses are assigned in sequence beginning from the outer periphery of a disk (from 0, 1, 2, . . . to yxe2x88x921). In addition, although not illustrated, sector addresses are assigned in the circumferential direction for each track on all recording surfaces. When recording data, if the data is too large to sequentially fit on a single track, another head or another cylinder track is assigned to accept the remainder of the data.
FIG. 2 shows the access sequence for a disk disclosed in the public release of Japanese Laid-Open Patent Number Hei 1-62886. In this example, there are four disks, which means that there are eight recording surfaces (two per disk).
As shown in FIG. 2, within each cylinder, the top surfaces and the bottom surfaces of each disk are alternately accessed in ascending order according to the head address. Thus, for cylinder 0, the heads are accessed in the following order 0, 1, 2, . . . 6, 7. After the final head (head 7) is reached, the top surface (head 0) of the adjacent cylinder will be accessed. As a result, if one sequential string of data does not fit on a single track, the head changes to the next head in the same cylinder, which performs the accessing upon the recording surface that is immediately below the previous recording surface. If the entire string of data cannot fit within that cylinder, the head and the cylinder will change, and accessing begins with the top surface of the adjacent cylinder.
FIG. 3 shows the accessing sequence based on the accessing method disclosed in the public release of Japanese Laid-Open Patent Number Hei 9-63199. In this example there are also four disks, which means that there are eight recording surfaces.
In the example shown in FIG. 3, the accessing sequence is substantially the same as that shown in FIG. 2 (whereby in each cylinder, the top surface and then the bottom surface of each disk are accessed alternately, and after the final head is reached, the adjacent cylinder is accessed). However, in the FIG. 3 example, when the cylinder changes, the head does not change as it does in the FIG. 2 example. Instead, in the FIG. 3 example, the adjacent cylinder on the same recording surface is accessed after the final head on a given cylinder has been accessed. The result is that in even-numbered cylinders, the heads are accessed in ascending order (0, 1, 2, etc.), while in odd-numbered cylinders, the head are accessed in descending order (7, 6, 5, etc.).
FIG. 4 shows the accessing sequence for the disk disclosed in the public release of Japanese Laid-Open Patent Number Hei 9-63202. In this case as well, there are four disks, which means that there are eight recording surfaces.
In the FIG. 4 example, the recording regions are accessed sequentially by cylinder address. Thus, head 0 accesses cylinders 0, 1, 2, etc. in ascending order until finally reaching the final cylinder (cylinder y). At that point, the head changes to head 1, and the recording surface immediately below is accessed, while remaining in cylinder y. Next, the cylinders are accessed by head 1 in descending order, until reaching cylinder 0, at which point the head changes to head 2, where the sequence continues as indicated in the figure. Thus, in general, in the FIG. 4 example, if sequential data does not entirely fit onto one track, the cylinder changes and the adjacent cylinder on the same recording surface is accessed. Further, if the data does not fit within that recording surface, the head changes and the track of the recording surface immediately below, but still within that same cylinder, is accessed.
In order to reduce the rotation wait time that accompanies the head movements when a cylinder changes, the sector numbers between tracks are offset and assigned. These offset sector numbers are referred to as the cylinder skew. In addition, in order to also reduce the rotation wait time that accompanies an access that covers different recording surfaces, the sector numbers between tracks are also offset and assigned. These offset sector numbers are referred to as the head skew.
When the access sequence shown in FIG. 2 is utilized, the head changes when moving within a single cylinder, as well as when changing from one cylinder to the adjacent cylinder. The amount of movement that accompanies a head change when changing from one cylinder to an adjacent cylinder can be determined by adding together the track pitch and the relative off-track amount between the head at the very top and the head at the very bottom. The relative off-track amount between different heads will depend on things such as the particular specifications of the disk drive device, the direction in which the disk drive device is installed, the temperature of the environment, and the core offset between the write head and the read head. With the narrow track disks that are recently being used, the relative off-track amount sometimes exceeds the track pitch. For this reason, when using the access sequence shown in FIG. 2, the cylinder skew is established by considering the worst case value of the relative off-track amount for the track pitch plus head 0 and the final head (head 7). As a consequence, if there is a large amount of variation in the relative off-track amounts, the amount of head movement that accompanies a cylinder change will be very large. In addition, a large cylinder skew must be established, which becomes a hindrance to increasing the transfer rate of the disk drive device.
In systems using the access sequence shown in FIG. 3, no head change accompanies a cylinder change because the cylinder change takes place without a change in the recording surface. As a result, the amount of head movement when the cylinder changes is fixed, when the servo data is recorded, to be within the range of the track pitch accuracy, and this is shorter than the access sequence shown in FIG. 2. However, since the head changes for each track change within the cylinder in FIG. 3 (as it does in FIG. 2), it is easy for head movement caused by the relative amount of offset of the heads to occur. Therefore, if there is a large amount of variation in the amount of relative offset of the head, the total amount of head movement will be greater, and a large head skew will have to be established. For this reason, no significant increase in the transfer rate can be anticipated by using the access sequence shown in FIG. 3, when compared to using the access sequence shown in FIG. 2.
Turning now to the access sequence shown in FIG. 4, here the cylinders are assigned to be accessed in sequence on the same recording surface. Because of this, in the majority of changes from one cylinder to the next cylinder during the recording process, there is not a change of head. The amount of head movement is fixed to be within the range of accuracy of the track pitch when the servo data is recorded. In addition, since the changing of the heads takes place in recording surface units (i.e., after all cylinders on a particular recording surface have been accessed), there are relatively fewer head changes (when compared to the sequences of FIGS. 2 and 3), reducing the impact of the relative offset of the heads. On the other hand, during the reading process, when a random access read process takes place within the range of a certain capacity, the head seek range will become greater than that discussed above, depending on the method of head movement, and this will lower the random access read performance. Accordingly, although the recording process of the FIG. 4 example is much faster than that of the FIG. 3 example, the FIG. 4 example has a longer access time during the read operation.
For these reasons discussed above, the first objective of this invention is to offer a disk drive device in which a high level of data transfer efficiency can be obtained.
Another objective of this invention is to shorten the head skew when the heads change.
These and other objects of the present invention are discussed or will be apparent from the following description of the present invention.
In the case of a magnetic head in which an MR element is used as the read head, the masks used to form the MR element are different for those used as the upper heads (which are used to record or regenerate on the top surface of the disk) than for those masks used for the lower heads (which are used to record or regenerate on the bottom surface of the disk). Additionally, the amount of offset in the center line of the read head and the write head is also different between the upper heads and lower heads. Further, the relative off-track amount between an upper head and a lower head is greater than the relative off-track amount for either the upper heads alone or for the lower heads alone. In the present invention, attention was directed to these factors in order to increase the data transfer rate by devising an improved head changeover sequence.
In order to resolve the problems indicated above, the preferred embodiment of the disk drive device of the present invention utilizes an accessing sequence which begins where only the top surfaces, within a single cylinder, of a plurality of disks are accessed. Next, only the bottom surfaces, within the same single cylinder, of a plurality of disks are accessed. After the bottom surfaces of that single cylinder have been accessed, the bottom surfaces of an adjacent cylinder are accessed, followed by the top surfaces of that same adjacent cylinder. According to this sequence, most head changes will take place between a series of upper heads or between a series of lower heads, which have a relatively small amount of relative offset. For this reason, the amount of head movement that accompanies a head change is minimized, which allows the head skew to be set to a relatively small value. As a result, the present invention accommodates an increase in the rate of data transfer. In particular, by either accessing all of the top surfaces of the plurality of disks in a single cylinder, or by accessing all of the bottom surfaces of the plurality of disks in that same cylinder, there will only be one head change, from the upper head to lower head, which increases the rate of data transfer.
Furthermore, since the access destinations of the sequential data will be assigned continuously across adjacent cylinders that are on the same recording surface, there is no head change for a cylinder change. Accordingly, the distance the head moves is fixed due to the range of the track pitch accuracy, restricting the cylinder skew to a minimum. In addition, when there is a head change, the cylinder skew can be shortened since it is no longer necessary to take into account the relative offset between the currently selected head and the head to which the change will be made. These factors also contribute to increases in the data transfer rate.
An additional feature of the present invention relates to the fact that, in the preferred embodiment, the recording surface of the disk is divided into a plurality of zones in the radial direction, and the number of disk rotations per minute or the number of recording cycles may be varied for each zone. Doing this allows the difference in cycle speeds between the outer circumference and the inner circumferences to be absorbed, which allows the recording surfaces to be used more efficiently. In this case, however, if there is an even number of cylinders within each zone, there will not be an inversion in the relationship between the physical cylinders and the logical cylinders (i.e., when moving from one zone to the next, odd numbered logical addresses will continue to be associated with odd numbered physical addresses, and vice versa).
Briefly, the present invention relates to a disk drive device that includes a plurality of disks that are arranged concentrically about a central axis, wherein each of the disks includes a plurality of concentric tracks of different diameters. Each of the disks also includes a top surface and a bottom surface. There are a plurality of cylinders defined by a combination of one of the tracks from each of the disks, wherein each cylinder consists of a plurality of tracks of a single diameter. A plurality of heads are associated with the disks, wherein each of the heads is configured and arranged to access either a top surface or a bottom surface of one of the disks. The present invention also includes an upper level device for issuing access commands directing the heads to access the disks. When an access command is issued that requires sequential data to be accessed on more than one track, an access sequence is followed in which at least two of the top surfaces on different disks of the same cylinder are accessed directly after each other, or, at least two of the bottom surfaces on different disks of the same cylinder are accessed directly after each other.